The present invention relates generally to an apparatus useful in the curing of retreaded tires exposed to elevated temperatures and pressures. More specifically, the present invention relates to an apparatus used to seal a conventional curing envelope to a tire casing to prevent deterioration of the retread covered by the envelope during the retread curing process.
It is well known to cure retreaded tires under elevated temperatures and pressures which occur in a tire autoclave. However, the superheated steam environment of the autoclave must not access the area of the tire to be retreaded. Thus the prior art discloses various devices used to seal an elastomeric protective envelope over the retread area of the tire, typically between a mechanical structure and the sidewall or side surface of the tire casing. Examples of such sealing systems used in retreading systems are described in detail in U.S. Pat. Nos. 2,966,936, 3,236,709, 3,802,978, 3,884,740, 3,895,985, 3,966,535, 4,129,474, 4,175,991, 4,242,169, 4,274,897 and 4,309,234.
It is also known in the art to seal the curing envelope by radially expanding a unitary ring which abuts the bead surface of the tire to be retreaded. In such devices the diameter of the ring, when in its unexpanded position, is slightly smaller than the diameter of the bead of the tire, allowing the ring to be easily placed within the tire casing; when the ring is expanded, the curing envelope is sealed between the outer surface of the ring and the bead of the tire. See, for example, U.S. Pat. Nos. 4,861,247 to Schimanek and 4,634,357 to Brewer, which are hereby incorporated by reference.
However, these prior art devices are difficult to adjust once they have been positioned, and do not provide effective ring expansion. For example, the use of a single ring having overlapping end portions tends to form a "C" shape when expanded, and thus cannot provide the circumferentially uniform seal which an expandable ring capable of maintaining a circular or nearly circular shape would provide against the bead or rim of a tire. Moreover, the prior art suggests the use of a relatively large spacing between the portions of the locking mechanism which operate to expand the ring.